The present invention relates to sensors that measure through the voltage induced by the time rate change of flux linkage in a sensing coil.
Sensors that measure through the voltage induced by the time rate of change of flux linkage in a sensing coil are susceptible to the corruption of their output voltage signal by stray or undesirable magnetic fields linking with the sensing coil. These types of sensors are typically used in electric machine speed sensing, crank shaft position sensing, cam shaft position sensing, input shaft transmission speed sensing, vehicle speed sensing and a.c. current sensing.
One solution for eliminating the effects of stray magnetic fields on the sensing coil would be to eliminate or decouple the voltage produced by the stray magnetic fields from the sensor output voltage using a computer, DSP, or even analog circuitry. However, matching the voltage produced by the stray magnetic field to sufficiently reduce their effects is extremely difficult.
Therefore, there is a need for a new and improved system and method for canceling the effects of stray magnetic fields on sensing coils. The new and improved system and method must cancel the effects of stray magnetic fields on the sensing coil without the need for complex circuitry or signal processing. Additionally, the new and improved system and method must also have packaging flexibility.
In accordance with an aspect of the present invention, a sensor system for sensing a rotation of a sensing wheel is provided. The sensor system has a sensing coil in juxtaposition with the sensing wheel. Moreover, the sensing coil has a sensing coil output signal indicative of the rotational speed of the sensing wheel. Further, a cancellation coil is located remotely from the sensing coil and connected in series with the sensing coil. Additionally, the cancellation coil has a cancellation coil output signal indicative of an environmental disturbance which is effecting the sensing coil output signal. The cancellation coil output signal operates to cancel the effects of the environmental disturbance on the sensing coil output signal.
In accordance with another aspect of the present invention, the sensing coil further comprises a permanent magnet.
In accordance with still another aspect of the present invention, the sensing coil further comprises a pole piece.
In accordance with still another aspect of the present invention, the cancellation coil further comprises a pole piece.
In accordance with still another aspect of the present invention, the cancellation coil is in juxtaposition with the sensing wheel.
In accordance with still another aspect of the present invention, the sensing wheel includes at least one tooth.
In accordance with still another aspect of the present invention, the cancellation coil is in axial alignment with the at least one tooth on the sensing wheel.
In accordance with still another aspect of the present invention, the cancellation coil is located an integer number of teeth away from the sensing coil.
In accordance with still another aspect of the present invention, the cancellation coil is located an integer number of electrical machine poles away from the sensing coil.
In accordance with still another aspect of the present invention, the cancellation coil is in axial alignment with the sensing coil.
In accordance with yet another aspect of the present invention, a method for canceling the effects of stray magnetic fields on a sensor system that senses a rotation of a sensing wheel includes sensing the rotation of the sensing wheel using a sensing coil, wherein the sensing coil has a sensing coil output signal indicative of the rotational speed of the sensing wheel. Further, an environmental disturbance which is affecting the sensing coil output is sensed using a cancellation coil located remotely from the sensing coil and connected in series with the sensing coil. Moreover, the cancellation coil has a cancellation coil output signal indicative of the environmental disturbance. The cancellation coil output signal cancels the effects of the environmental disturbance on the sensing coil output signal.
The above features, benefits and advantages and other features, benefits and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken together with the accompanying drawings.